The major objective of this project is to demonstrate the role of the brain capillary in providing a viable environment for primary and secondary tumors of the nervous system. Blood-brain barrier function of biologically important substances and local blood flow will be examined with the indicator diffusion and brain uptake techniques. In this manner the physiological and morphological substrate of the blood-brain barrier will be evaluated and related to cerebral function and metabolism in various experimental conditions. These conditions include low and high LET radiation (-pi meson) as well as experimentally (viral) induced brain tumors. It is proposed that changes in BBB occur in central nervous system tumors and are related to the metabolic and functional requirements of the tumor, and therefore suggest the direction of therapeutic strategy.